The present invention relates to the separation of an image a portion of which can then be used in the production of a composite image and, more particularly, to the separation of an image for use in the production of a composite image using two or more video images.
Key insertion makes it possible to insert a part of one television image into another to produce a special effect. For example, it is quite common in studio broadcasting to combine an image taken in the studio, typically of an announcer, with one or more background images of various scenes, typically outdoor scenes. The scenes may be produced in real time by a second television camera, they may be pre-recorded still or moving images taken earlier by a television camera, or they may be computer generated images, among other possibilities.
Combining the image of a studio announcer with some other scene gives the viewer the impression that the announcer is present at the scene and/or gives the viewer further information. The use of keying is convenient as it obviates the need for the announcer to be physically present at the actual scene, which may be distant or otherwise not readily accessible, and further obviates the need for installing and periodically replacing a physical image-bearing backdrop behind the announcer.
Various techniques are known for combining video images. Perhaps the most popular is the chroma-key insertion technique, also known as color separation overlay technique. In the chroma-key technique, a television camera is trained on an announcer, or other studio actor, who is located in front of a colored backdrop, which is typically blue. The images from this camera, as well as background images from any of number of suitable sources, are fed to a processor which is able to combine the two images to form a single image. The processor replaces the colored (typically blue) portions of the studio image with the background image to form a combined image featuring the announcer, or other studio actor, surrounded by portions of the background images.
Various attempts have been made to improve the chroma-key technique. Representative of patents describing variations of the chroma-key technique are U.S. Pat. Nos. 4,163,992, 4,202,008 and 4,393,394.
The chroma-key technique, while in widespread use, suffers from a number of disadvantages which limit its versatility. The technique requires the use of a special studio equipped with the proper blue backdrop and suitable lighting systems which satisfy stringent requirements. This limits the applicability of the system to a number of specially equipped studios so that it is not possible to use the technique in less sophisticated studios or outdoors. Furthermore, care must be taken to avoid use of the keying color (typically blue) in the studio. Thus, care must be taken to ensure that the announcers, actors, and every other person or object forming a part of the studio image is completely devoid of the blue color since such presence of the keying color would lead to the highly undesirable substitution of the background image onto undesirable portions of the studio image.
There is thus a widely recognized need for, and it would be highly advantageous to have, a technique for combining video images which would have advantages in the above respects.